In copending U.S. patent application Ser. Nos. 10/137,391 filed May 3, 2002 (WO 02/089597) and 10/476,230 filed Jun. 9, 2004, all assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a process for producing a protein isolate of high purity, containing at least about 100 wt % protein when determined by the Kjeldahl or equivalent method as percent nitrogen (N) and multiplied by a conversion factor of 6.25. As used herein, the term “protein content” refers to the quantity of protein in the protein isolate expressed on a dry weight basis. In the aforementioned U.S. Patent Applications, the protein isolate is made by a process in which oil seed meal is extracted with a food grade salt solution, the resulting protein solution, after an initial treatment with a colourant adsorbent, if desired, is concentrated to a protein content of at least about 200 g/L, and the concentrated protein solution is diluted in chilled water to form protein micelles, which are allowed to settle to form an aggregated, coalesced, dense amorphous, sticky gluten-like protein isolate mass, termed “protein micellar mass” or PMM, which is separated from residual aqueous phase and may be used as such or dried.
In one embodiment of the process described above and as specifically described in U.S. patent application Ser. Nos. 10/137,391 and 10/476,230, the supernatant from the PMM settling step is processed to recover a protein isolate comprising dried protein from wet PMM and supernatant. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes, mixing the concentrated supernatant with the wet PMM and drying the mixture. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, protein (N×6.25).
In another embodiment of the process described above and as specifically described in application Ser. Nos. 10/137,391 and 10/476,230, the supernatant from the PMM settling step is processed to recover a protein from the supernatant. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes and drying the concentrate. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, protein (N×6.25).
The procedures described in the aforementioned US Patent Applications are essentially batch procedures. In copending U.S. patent application Ser. No. 10/298,678 filed Nov. 19, 2002 (WO 03/043439), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a continuous process for making canola protein isolates. In accordance therewith, canola oil seed meal is continuously mixed with a salt solution, the mixture is conveyed through a pipe while extracting protein from the canola oil seed meal to form an aqueous protein solution, the aqueous protein solution is continuously separated from residual canola oil seed meal, the aqueous protein solution is continuously conveyed through a selective membrane operation to increase the protein content of the aqueous protein solution to at least about 200 g/L while maintaining the ionic strength substantially constant, the resulting concentrated protein solution is continuously mixed with chilled water to cause the formation of protein micelles, and the protein micelles are continuously permitted to settle while the supernatant is continuously overflowed until the desired amount of PMM has accumulated in the settling vessel. The PMM is removed from the settling vessel and may be dried. The PMM has a protein content of at least about 90 wt % (N×6.25), preferably at least about 100 wt %.
The meal which is extracted at the initial step in the preparation of the protein isolate contains a number of components which can contribute to the taste and colour of the protein isolate. For example, there are hull particles that contain certain phenolic compounds which may leach into the extract. Such phenolic compounds are prone to oxidation to form coloured compounds.
Other components which may contribute to the quality of the meal and its products are glucosinolates and the products of their degradation. Degradation of glucosinolates is catalyzed by degrative enzymes called myrosinases, which break down glucosinolates into isothyocyanates, thiocyanates, nitriles and elemental sulfur. The degradation products of glucosinolates reduce the value of glucosinolate containing plants when used as food for humans or for feeding animals.
Canola is also known as rapeseed or oil seed rape.